Coaxial transmission line terminal



June H. GRANGER 2,32 23 COAXIAL TRANSMISSION LINE TERMINAL Filed May 2, 1941 V x mater INVENTOR.

Ha ro/d Granger 0 Ora-140 591) g'romvsv Patented June 22. 196

UNITED STATES PATENT OFFICE zszzsn coaxial. rasssmssrosnmnnaumsr.

mm Granger, United States Marine Corps Application May '2, 1941, Serial No. 391,4"

scams. (Cl. 174-19) (Grantednnder the act oi March 8, 1888, as

amended April 30, 1928;.3'" 0. G. 78'!) My invention relates to a coaxial transmission line terminal and, more particularly, to a terminal of the stated character that maintains its fluid-tight integrity unimpaired in use and provides a convenient means for connectin electrical conductors thereto.

As is well known, coaxial transmission lines are employed for the transmission or reception of radio frequency energy because of the many structural and electrical advantages inherent therein. Among the advantages possessed by coaxial transmission lines are the maintenance by the same 01 substantially uniform electrical characteristics under all service conditions and the ability to increase the power transmission thereof either by the partial evacuation of or by the introduction of gas under pressure into the space between the outer and inner concentric conductors, g i a In order to insure the retention of the above enumerated advantages, it is essential that the coaxial transmission line be provided with a terminal that maintains its fluid-tight integri unimpaired in use. This is achieved in accordance with the present invention by the provision oi a terminal comprised of a pair of insulatingly spaced concentric metallic conductors and a lay: er of glass for sealing one conductor-fto-"the other.

' The glass has .a low dielectric loss at radio irequenciesanda temperature coeiiicient of expansionsubstantially equal to that of the metallic conductors to thus insure a vacuum-tight seal.

The inner conductor oi'the concentric termirial pair may be tubular, if desired, to thus provide a ready means for partially evacuatingthe space between the outer and inner conductors v of the transmission line or for introducing gas under pressure into the space therebetween. A

suitable connector electrically continuous with the inner conductor of the concentric terminal pair may be supported in an insulating manner from a metallic sleeve secured to the outer conductoroi the concentric terminal pair and extending beyond the seal therebetween. This is a feature of importance in the present invention since the sleeve not only provides 'a' protec: tive covering for the seal but also takes the mechanical stresses that would otherwise be imposed upon the seal through the securement or conductors to the connector or otherwise.

In the light of the foregoing, it is among the several; of my invention to provide a coaxial on line terminal in which fluidtight integrity is achieved through the utilisation of a glass-io-metal seal; to provide a terminal ot the stated character through which gas may be conveniently introduced into or withdrawn from the transmission line; and to provide a terminal or the character noted above which incorporates a novel arrangement 01' parts (or protecting the glass-to-metal seal and for facilitating the connection of conductors to the transmission line.

Other objects and many oi the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description whenconsidered in connection with the accompanying sheet of drawing, wherein: Fig. 1 is a view in partial sectional elevation of one embodiment oi the terminal oi the presv ent invention shown connected to the transmission line and as incorporating an inner gas conveying conductor;

Fig. 2 is a view in partial sectional elevation oi another embodiment of the terminal of the present invention shown connected to the transmission line and as incorporating a solid inner conductor;

Fig." 3 is a view in partial sectional elevation of the novel arrangement of parts that may be I employed in conjunction with either of the embodiments depicted in Figs. 1 and 2 for protecting the glass-to-metal seal and' for facilitating the connection of conductors to the transmission line; and I o t i Fig. 4 is a view in end elevation of the structure delineated in Fig. 3.

Turning now to Fig. l or the drawing, there is shown depicted therein a coaxial transmission line terminal identified in generalby the reference character i and comprised of the pair of insulatingly spaced concentric metallic conductors 2 and l sealed together by the layer 0! glass 4. The glass I has a low dielectric low at radio frequencies and a temperature coefllcient of enpansion substantially equal to that or the metalliczconductors I and 3, as willbe pointed out more in detail hereinafter.

2 Thecoaxial transmission line 5 is shown with its inner conductor I in telescoping and ,electrically continuous engagement with the inner til-- bular gas conveying conductor 2 o! the concen -tric terminal pair. electrical continuity being achieved by soldering or otherwise securingthe telescoping conductors I and t at their iunction point; A metallic sleeve I is secured in fluidtight relation tothe open end of the outer conductor'l o! the tr line and to the Outer concentric conductor I of the terminal pair in any suitable manner, as by sweating or welding the sleeve I and the outer concentric conductors 3 and l at their Junction points. A pressure gauge I of any conventional prior art construction may be optionally employed to indicate the pressure of the gas between the inner and outer concentric conductors l and I of the t line I.

The inner gas conveying conductor 2 of the concentric terminal pair is suitably apertured at I. by providing a number 01' diametrical perforations through the conductor so that gas may be easily introduced within or withdrawn from the transmission line. By virtue of this construction it is possible to provide the transmission line with dry air or a dry inert gas at or above atmospheric pressure or to evacuate the transmission line to. any desired degree of pressure. After the desired gas pressure is atablished within the transmission line, the inner tubular conductor 2 of the terminal pair is her,- metically sealed in any suitable manner as by crimping the same and soldering the conductor at the crimped portion.

The embodiment depicted in Fig.2 of the drawing is in all respects identical with that of Fig. 1 except that the inner concentric conductor 2 of the terminal I is solid instead of tubular and that the sleeve I is provided with a connection H for introducing or withdrawing gas from the transmission line B. I After the desired pressure is established within the transmission line, the terminal portion ll integral with the 'sleeve 1 may be sealed in any suitable manner. As shown in Fig. 2 of the drawing, the inner conductor 2 or the terminal and the inner conductor of the transmission line are butt welded at l2 or otherwise suitably secured at this point to establish electrical continuity therebetween. with the exceptions noted above the construction in Fig. 2 is identical with that of Fig. 1.

Hence, similar reference characters have been employed in both 4 these losses are principally due to dielectric hysteresis. The electrical energy lost as a result of dielectric hysteresis appears in the form of heat generated within the dielectric, the heat so generated being cumulative in part and resulting in 'higher temperatures within the dielectric with increase in the electrical losses.

In order, therefore, to insure a vacuum-tight seal in the terminal or the present invention. i s essential that the dielectric material I have a low loss at radio frequencies, a high melting point, high resistance to thermal shock and a coeiiicient of expansion substantially equal to that of the metallic conductors 2 and I sealed thereto. In accordance with the Present invention I employ as the dielectric sealing. material 4 glasses having the above cited characteristics and in particular the hard glasses because of their lower dielectric loss atradio frequencies.

sistance to thermal shock. Thus, they will with asaasss stand sudden changes of temperature without fracture.

By way of illustration there are tabulated below a number of hero-silicate glasses that may I Lowest temperature at which strains will deny to an inapprcciable value after exposure for fifteen hours.

While tungsten and molybdenum have coeiilcients of expansion of the right order of magnitude for sealing to the boro-silicate glasses and hence may be employed in the fabrication of the concentric terminal conductors 2 and I to form an emcient vacuum-tight seal, they possess the Timi- II Compositions and properties oi some alloys Compositions Expansivit 25 to 326 5. Per Per Per Per Per Y cent cent cent cent cent Ni 00 Fe Mn C l 0.2)(10' 'C. 32 16 51.1. 0.80 0. l0 2 000 6.- 2s 17 53. a o. 20 0. 2o 3 3.0XIO"/O.. 29.8 15.5 54.18 0. 22 0. 30

In order to make a successful seal, the memclents of expansion of the metal and the glass must be substantially the same over the temperature ranges within which the metal and glass areboth elastic. A large difference in the coefiicients of expansion produces stresses which may cause the glass to crack when cooled to room temperature and thus destroy the vacuum-tight seal. Some degree of diiierential expansion, however. between the metal and glass may be tolerated and is even desirable. Thus, it has been found that the alloys designated by the numbers 1, 2 and 3 in Table II above may be sealed respectively to the glasses designated by the numbers 1, 2 and 3 in Table I- to form therewith a vacuum-tight joint under the conditions encountered in use. a

For protecting the glass-to-metal seal and for facilitating the connection of conductors to the transmission line, the construction depicted in Figs. 3 and 4 may be employed with either of the embodiments heretofore described. As shown more particularly in Fig. 3, a metallic sleeve II is firmly secured in any suitable manner as by welding or sweating to the outer conductor 3 of the terminal pair and extends well beyond the seal 4 therebetween to thus form a protective housing for the same. An electrical insulator ll of any suitable material, such as a ceramic. material, is longitudinally apertured and terminally recessed to receive respectively the conductor 2 and the connector l5 electric-ally continuous therewith. The insulator H as shown is securely aflixed to the sleeve It in any convenoperation of my invention and have illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

The invention herein described and claimed may be used and manufactured by or for the lent manner as by crimping the sleeve firmly at between. One-or more nuts it are in threaded engagement with the sleeve |6- so that a good electrical connection may be made to a conductor by interposing and clamping the same between the disc I1 and the nut i'l next adjacent thereto. Since the connector I! is soldered or sweated to the conductor 2 and has a portion thereof embedded in the terminal recess 01 the insulator H, a rigid and secure mounting is provided for the same.

By virtue of the foregoing construction, the glass-to-metal seal is protected against mechanical shocks and hazards. sleeve I! provide a protective covering for the seal I but it also takes the mechanical stresses.

that would otherwise be imposed upon the seal through the securement of the conductors to the connector I! or otherwise. 'Finally, the construction delineated in Fig. 3 provides a very convenient means for connecting a conductor to the transmission line.

For not only does thesaid insulator, the said connector being electri-' According to the provisions of the patent statutes, I have set forth the principle and modeof Government of the United States of America for governmental purposes without the-payment of any royalties thereon or therefor.

I claim:

1. A coaxial transmission line terminal comprising in combination a pair 01' insulatingly spaced concentric metallic conductors and a layer oi! glass for sealing one conductor to the other, the said glass having a low high frequency dielectric loss and a temperature coeflicient oi. ex-

pansion substantially equal to that oi the metallic conductors, a tubular metallic conductor secured to the outer conductor of-the concentric conductor pair and extending beyond the seal therebetween, an insulator afllxed to the tubular metallic conductor and a connector supported from said insulator, the said connector being electrically continuous with the inner conductor of the concentric conductor pair.

2. A coaxial transmission lineterminal comprising in combination an inner tubular gas conveying metallic conductor concentric with and insulatingly spaced from an outer tubular metallic conductor and a layer of glass (or sealing one conductor to the other, the said glass having a low high frequency dielectric loss and a temperature coefllcientot expansion substantially equal to that of the metallic conductors, a metallic sleeve secured to the 'outer tubular conductor of the concentric conductor pair and extending beyond the seal therebetween, an insulator aflixed to the sleeve and a connector supported. from cally continuous with the inner tubular conductor oi the concentric conductor pair.

- HAROLDGRANGER. 

